1. Field of the Invention
The present invention relates generally to devices for measuring the quantity, or more accurately the depth or pressure head, of a volume of liquid in a container. More specifically, the present invention relates to air bubble tube or xe2x80x9cpurgexe2x80x9d type systems, wherein a gas is pumped to the bottom of the liquid tank and the pressure of the gas is measured to determine the pressure head, and thus the depth, of the liquid in the tank.
2. Description of the Related Art
The determination of a liquid quantity in a tank or other container is of great importance in a number of different fields, including the bottling and beverage industry (in both manufacturing and retail levels), vehicle fuel systems, closed lubrication systems, and a number of other applications. Accordingly, a number of different principles of measuring the quantity of a liquid in a tank or container, have been developed in the past. These different principles range from a simple calibrated stick, rod, or sight gauge, to float and arm type systems (as commonly used in vehicle fuel tanks), capacitance type systems for certain liquids, pressure sensing transducers disposed in the container bottom, to air bubble or xe2x80x9cpurgexe2x80x9d type systems related to the present invention.
The air bubble or purge system operates essentially by providing pressurized air, which is forced through a tube extending downwardly to the bottom of the tank or container. When the air pressure is slightly above the liquid pressure at the tube outlet, the air pressure will force air bubbles from the lower or outlet end of the tube, thereby stabilizing the air pressure within the tube. This air pressure may then be equated to the pressure head of the liquid, and thus the depth of the liquid in the container. By knowing the volume of the container, a determination of the quantity or volume of liquid in the tank or container is made.
However, such purge systems as developed in the prior art have various drawbacks and deficiencies. Conventionally, such purge systems have relied upon a separate mechanical pressure regulator, which regulates pressure from a relatively high pressure source (pneumatic pump, compressed air source, etc.). Where a motor is used to supply the air pressure for such systems, the motor must be somewhat larger and more powerful than required to produce pressure sufficient to equal the pressure head of the liquid, as the motor must provide sufficient additional pressure over and above the regulated pressure. This, and the fact that the motor must run continuously, result in considerable energy usage and render such systems impracticable for many applications. Moreover, the mechanical regulators used in such systems are relatively delicate, requiring frequent adjustment due to vibration, ambient temperature and pressure changes, etc, and thus are not suitable for installations in vehicles, factory lines, etc.
Thus, a need will be seen for an air bubble or purge type liquid measuring system which overcomes these and other deficiencies in the prior art. Rather than using a continuously operating motor to supply the air pressure for the system, the present invention actuates the pneumatic motor only as necessary to supply air (or other gas) to the down tube or dip tube which extends into the liquid tank or container. The motor is controlled by a precision regulator and novel electrical and pneumatic circuitry providing such precision control. The present purge type system is capable of providing liquid depth sensing to extremely precise tolerances if desired, on the order of the diameter of a single bubble escaping from the dip tube. This, and other features, provide numerous advantages in the bottling industry, auto manufacturing industry, and other areas where precision filling of containers is required.
The present depth sensing system also lends itself well to applications in vehicle fuel tanks and systems, as the present system does not require any electrical wiring or circuitry within the fuel tank or system. The only intrusive elements within the tank or container, are the dip tube and vent tube which supply the pressure information to the sensing apparatus. Heretofore, such systems were impracticable for use in such vehicle fuel systems due to their weight, bulk, energy usage, maintenance requirements, and relative lack of sensitivity due to the relatively large continuous use motors required and the regulators used. The present system provides numerous advantages over such prior art devices.
A discussion of the related art of which the present inventor is aware, and its differences and distinctions from the present invention, is provided below.
U.S. Pat. No. 1,731,928 issued on Oct. 15, 1929 to Edward E. Johnson, titled xe2x80x9cConstant Liquid Level Apparatus,xe2x80x9d describes a device, for maintaining an essentially constant liquid level within a closed tank, filling the tank as the level drops and shutting off flow to the tank as the level rises to the point desired. The Johnson system operates on an entirely different principle than the purge line system of the present invention, with Johnson utilizing a pair of complementary mercury type switches in his system. Moreover, Johnson does not disclose any means of displaying the depth of the liquid in the tank, as he has no motivation to do so due to the constant level maintained by his system.
U.S. Pat. No. 2,502,578 issued on Apr. 4, 1950 to John I. McDaniel, titled xe2x80x9cLiquid Level Control Device,xe2x80x9d describes a system utilizing a pair of electrodes within a tank. When the liquid level drops below the lower electrode, a motor is energized to pump liquid into the tank. When the liquid level reaches the higher electrode, the motor is shut off. The McDaniel device thus uses an entirely different principle of operation from that of the present invention, and controls the liquid level only through a relatively broad range determined by the difference in heights of the two electrodes. Moreover, McDaniel does not provide any display of liquid quantity with his system.
U.S. Pat. No. 2,734,458 issued on Feb. 14, 1956 to Thomas B. Hayes, titled xe2x80x9cPump Speed Control Arrangement,xe2x80x9d describes a compound system controlling a pump motor primarily by means of a xe2x80x9cliquid rheostatxe2x80x9d (i. e., a series of capacitor plates) within the tank. The capacitance of the plates varies as the liquid level varies, thereby controlling the speed of an output pump motor. Hayes also utilizes a pair of floats, with the lower float cutting off the motor and the higher float causing the motor to run at maximum speed. The inclusion of electrical components within the tank, and the lack of any liquid level display, both teach away from the present invention with its purge type system providing an extremely accurate readout of liquid level in a tank or container.
U.S. Pat. No. 3,213,795 issued on Oct. 26, 1965 to John W. Parks et al., titled xe2x80x9cFluid Handling System,xe2x80x9d describes a bubble tube or purge type device wherein pressure from the pneumatic system is supplied to a smaller tank having two compartments. The first compartment receives the pneumatic pressure, while the second compartment contains a series of capacitance plates (xe2x80x9cliquid rheostatxe2x80x9d) therein. When the level of the main tank drops, the pneumatic pressure drops, causing the level of the auxiliary tank first chamber to rise and the second chamber to fall, thereby exposing more of the plates to control a reduction in the pump motor speed. The pneumatic motor runs constantly, unlike the present invention, to provide the required air supply to operate the system. Moreover, Parks et al. do not provide any display of the liquid level in the tank(s).
U.S. Pat. No. 3,794,789 issued on Feb. 26, 1974 to Johnnie J. Bynum, titled xe2x80x9cPressure Sensitive Control For Pump Regulator,xe2x80x9d describes an electrical pump control circuit which shuts down the liquid pump in the event the pump cannot draw sufficient liquid, thereby preventing pump motor burnout. The Bynum system operates by measuring the pneumatic pressure captured within a closed tank. If the pressure drops to a certain point, indicating that the liquid volume in the tank has dropped and allowed the air volume in the tank to expand, a circuit shuts off the pump motor. Bynum does not use a bubble pipe or purge system for measuring the depth of the liquid in the tank, as provided by the present invention, and moreover, Bynum does not provide any display of the liquid quantity within the tank.
U.S. Pat. No. 3,937,596 issued on Feb. 10, 1976 to Robert O. Braidwood, titled xe2x80x9cFluid Pump Driving Control,xe2x80x9d describes a purge type system for controlling the operation of a hydraulic pump, which in turn controls a liquid pump motor. The air pump for the Braidwood system must operate continuously in order to supply pressure to an electromechanical regulator. The regulator in turn controls the swash plate of the hydraulic pump in order to control the hydraulic output of the pump and speed of a corresponding hydraulic motor which drives the liquid pump. As in other purge type systems noted above, Braidwood uses the purge system only to control a liquid pump, either directly or indirectly, to control the liquid level within a container. Braidwood does not disclose an intermittently operating air pump nor any quantity display.
U.S. Pat. No. 4,176,550 issued on Dec. 4, 1979 to Charles L. McClure, titled xe2x80x9cDepth/Flow Monitoring Instrumentation, xe2x80x9d describes a bubble tube or purge type system utilizing pressurized gas, i. e., xe2x80x9crefrigerant cans,xe2x80x9d col. 2, line 43. Accordingly, McClure does not provide any form of motor and pneumatic pump for his system. While McClure does provide a means of recording the gas pressure, and thus the pressure head or depth of the liquid, he does so only with a recording chart which is driven by a xe2x80x9csensing element.xe2x80x9d Such a chart provides only a history of liquid depth, and is not suitable for use as a quantity gauge (e. g., fuel gauge, etc.), as provided in the present invention. Moreover, the McClure system is only adaptable to a closed container, whereas different embodiments of the present system may be adapted to open tanks as well.
U.S. Pat. No. 4,297,081 issued on Oct. 27, 1981 to William A. Irvin, titled xe2x80x9cLiquid Level Control System,xe2x80x9d describes a purge level sensing system which supplies pneumatic pressure to a mercury manometer. The manometer in turn controls a series of relays which actuate one or more liquid pump motors, depending upon the height of the column of mercury. The Irvin system requires the pump motor to run continuously, unlike the intermittent motor operation provided by the present invention. While Irvin provides an approximate form of level indication by means of a series of warning lights indicating which motors are operating and high and low level alarms, he does not provide a continuously incremental gauge display of the liquid level, as in the present invention.
U.S. Pat. No. 4,972,709 issued on Nov. 27, 1990 to James R. Bailey, Jr. et al., titled xe2x80x9cPump Control System, Level Sensor Switch And Switch Housing,xe2x80x9d describes a float type control system for use in the downhole of an oil well. The Bailey, Jr. et al. system does not utilize any form of bubble purge principle, as provided in the present invention. Moreover, Bailey, Jr. et al. do not provide any means of displaying the level of a liquid in a tank or other container, as provided by the present invention.
U.S. Pat. No. 5,059,954 issued on Oct. 22, 1991 to Paul M. Beldham et al., titled xe2x80x9cLiquid Level Sensing System,xe2x80x9d describes a purge type system for distinguishing between line losses or leaks, and actual depletion of the liquid in the tank. The Beldham system operates the purge pump motor only periodically, with the pump building pressure as desired. If the pressure builds up relatively rapidly, a leak in the system is indicated and an alarm is provided to indicate the need for maintenance. Slower pressure buildup indicates normal depletion of the liquid in the container, with no maintenance being required. The Beldham et al. system does not actuate the purge pump motor to maintain a constant pneumatic pressure very slightly above the liquid pressure head, as provided by the present invention. Rather, Beldham et al. allows pressure in the system to bleed down periodically. This results in an inaccurate indication of the liquid level or height in the tank. In contrast, at least one embodiment of the present system provides an accurate display of the liquid level at all times, thereby serving as an accurate fuel or other quantity gauge, etc.
U.S. Pat. No. 5,163,324 issued on Nov. 17, 1992 to Glen A. Stewart, titled xe2x80x9cBubbler Liquid Level Sensing System,xe2x80x9d describes a system in which the pneumatic pump motor is periodically cycled by means of a timer, rather than according to demand for pneumatic output as in the present system. Stewart cycles his pump on and off by means of a timer, which results in the quantity display failing to be updated during those periods when the timer has shut down the pump. In contrast, the present system is also adaptable for use in a vehicle fuel system, and provides a continuous and accurate readout or display of the fuel quantity in the tank. Moreover, the Stewart system periodically vents the pneumatic pressure and vapor return lines to the atmosphere. This is unacceptable in most vehicle fuel tanks, where capture of fuel vapors is required by Environmental Protection Agency regulations. The present system may be used with an open tank, but the vapor return line (ambient tank pressure) returns to the interior of the fuel tank, rather than selectively venting to the atmosphere, as in the Stewart system. The present invention also includes a novel lower or outlet end configuration for the dip tube within the tank, which configuration is not disclosed in any of the prior art of which the present inventor is aware. This outlet end configuration provides a relatively large volume which results in extremely rapid reactions to pressure changes in the system, e. g., as the tank is filled, to actuate the pneumatic motor to preclude entry of fuel into the pneumatic system.
Soviet Patent Publication No. 939,947 published on Jun. 30, 1982 describes (according to the English abstract) a bubble or purge type liquid depth measuring system utilizing compressed air for supplying the air within the down tube of the system. The device of the Soviet Patent Publication is particularly adaptable to relatively large and rapid changes in the depth of the liquid being measured, and hence utilizes relatively highly pressurized pneumatic sources. As a result, the device of the Soviet Patent Publication does not have a pneumatic pump motor and is more closely related to the device of the ""550 U.S. Patent to McClure, discussed further above, than to the present invention. Also, no disclosure of any means for displaying the depth of the liquid is apparent in the Soviet Patent Publication.
Japanese Patent Publication No. 60-210,724 published on Oct. 23, 1985 describes (according to the English abstract) the basic principle of purge pipe liquid depth measurement. The ""724 Japanese Patent Publication utilizes an inlet valve for regulating pressure from a pneumatic source upstream of the valve. Thus, the supply pressure must be higher than required for filling the dip tube in the tank, thus requiring a larger and heavier motor (or compressed air tank) than that required by the present invention, which regulates pressure by controlling the pneumatic pump motor, rather than reducing pressure downstream of the motor and pump. Moreover, no liquid level display means is apparent in the ""724 Japanese Patent Publication, whereas such display means is a part of at least one embodiment of the present invention.
East German Patent Publication No. 279,947 published on Jun. 20, 1990 describes (according to the English abstract) a purge type system incorporating intermittent measurement. Gas is blown through the pneumatic system according to predetermined measured values, time, or system pressure. The present invention utilizes system pressure to control the operation of the motor driving the pneumatic pump of the system, but the intermittent actuation of the motor occurs on demand to keep the down tube filled with air continuously, thus providing a continuous reading of the pressure within the tube, and corresponding depth of the liquid, at all times. Moreover, no means of displaying the liquid depth or quantity is apparent in the ""947 East German Patent Publication, while such display means is a part of at least one embodiment of the present invention.
Japanese Patent Publication No. 2-259,428 published on Oct. 22, 1990 describes (according to the English abstract) a purge type system utilizing a continuously operating pneumatic pump motor with a restrictor or regulator in the line downstream of the motor and pump. The disadvantages of such continuously operating systems and the relatively large motors required, have been noted further above. In addition, no means of displaying the depth of the liquid is apparent in the ""428 Japanese Patent Publication. Also, the ""428 Japanese Patent Publication teaches away from the down tube outlet of the present invention, by providing a relatively narrow outlet nozzle at the bottom end of the device. The present system controls bubble size and output by means of motor operation, instead.
Finally, pages 5-16 through 5-18 of an undated copy of xe2x80x9cProcess Instruments And Controls Handbookxe2x80x9d (McGraw-Hill Book Co.), second edition, describe various means of measuring the head pressure or depth of a quantity of liquid. Page 5-18 describes the conventional air bubble tube or purge system, upon which the present invention is based. This description teaches away from the present invention, in that it states that xe2x80x9cair pressure is set at a value slightly greater than the hydrostatic pressure for maximum level and its rate of flow adjusted by the needle valve . . . xe2x80x9d While the present system may incorporate a needle valve for flow adjustment, the present system utilizes the pressure transducer of the system to provide a signal to the motor for actuation or stopping. The motor thus need not be larger than that required to provide just the proper pressure to equal the pressure head of a full tank or container, and also need not run continuously, as in the case of the system described in the Process Instruments Handbook. Moreover, this publication states on page 5-16 that xe2x80x9cThe minimum range of measurement with conventional pressure gages employing a sensitive spring and bellows assembly is about 0 to 5 in. of water.xe2x80x9d The present invention, with its incorporation of solid state transducer devices and novel motor operation, provides accuracies on the order of one to two orders of magnitude better than that stated in the Process Instruments Handbook.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed.
The present invention comprises various embodiments of a liquid depth sensing system which utilizes the bubble tube or purge pipe principle of operation. The present purge system provides at least two distinct improvements over such systems which have been developed in the past, enabling the present system to provide considerably greater accuracy and response time for certain operations (bottling, etc.). Significantly greater accuracy is provided by eliminating the conventional electromechanical pressure regulator, and operating the pneumatic pump motor by means of a pressure transducer and novel circuit so the motor not only provides the required pressure, but also acts to regulate the pressure by means of intermittent operation as controlled by the electrical circuit of the present invention. This much greater accuracy enables the present purge system to be used in applications where relatively small changes in liquid depth or head pressure must be measured, such as vehicle fuel tanks, bottling operations, etc.
Another significant advance over the prior art is the provision of a xe2x80x9cbell,xe2x80x9d or larger volume portion, at the lower end of the dip tube. This larger volume entraps a greater volume of air or gas in the lower end of the dip tube. This is particularly valuable during bottling operations or in any situation where rapid filling of a container must be accomplished. The air or gas pressure within the dip tube (and bell portion) will always equal the head pressure of the liquid surrounding the dip tube. Thus, the total volume of air or gas within the widened bell portion of the tube will be proportional to the head pressure. In bottling operations, where the head pressure of the liquid varies only over several inches, the air or gas is compressed very little, and essentially retains its original volume. However, the gas within the bell portion of the tube is forced upwardly in the tube to a height or extent greater than that of the upper surface of the liquid during a rapid filling operation, due to the relative constriction of the narrower dip tube. This results in the pressure signal from the rising liquid level, being transmitted to the transducer much more rapidly than occurs in a conventional system. The transducer thus may provide a much more rapid shutoff of the incoming liquid. This enables the bottle or container to be filled at a much faster rate than was heretofore possible, and still achieve the required accuracy.
Accordingly, it is a principal object of the invention to provide an improved liquid depth sensing system for rapidly and precisely measuring the depth or pressure head of a liquid, for determining the quantity of a liquid in a container, bottling operations, and other related applications.
It is another object of the invention to provide an improved liquid depth sensing system which incorporates the bubble tube or purge principle of operation, with the interior of the tank or container incorporating the present system being devoid of any electrical componentry associated with the present system for safe measurement of combustible liquids in a tank or container.
Another object of the present invention is to provide an improved liquid depth sensing system which is adaptable to either open or closed tanks or containers.
It is a further object of the invention to provide an improved liquid depth sensing system utilizing a pneumatic motor and pump as the pressure regulating means of the device and eliminating a conventional pressure regulator, thus providing extremely accurate operation under adverse conditions for motor vehicle, factory line, and other harsh operating environments.
An additional object of the invention is to provide an improved liquid depth sensing system adaptable to any orientation and to a broad range of temperatures due to the use of solid state componentry and elimination of electromechanical regulating means.
Still another object of the invention is to provide an improved liquid depth sensing system incorporating a bell mouth in the dip tube for more rapid response during bottling or other filling operations.
It is an object of the invention to provide improved elements and arrangements thereof in an apparatus for the purposes described which is inexpensive, dependable and fully effective in accomplishing its intended purposes.
These and other objects of the present invention will become readily apparent upon further review of the following specification and drawings.